1. Field of Invention
The present invention relates to a valve train layout structure, and more particularly, to a valve train layout structure including a cam phaser and a camshaft-in-camshaft.
2. Description of Related Art
Internal combustion engine generates power by sucking fuels and air into a combustion chamber and combusting them. An intake valve is opened by a driving camshaft and while the intake valve is opened, the air or mixture of fuel and air is sucked into the combustion chamber. Further, an exhaust valve is opened by the driving camshaft after combustion and while the exhaust valve is opened, combustion gas is discharged out of the combustion chamber.
Optimum operation of an intake valve and an exhaust valve is adjusted depending on rotating speed of an engine. This is because adequate valve lift or opening/closing timing of a valve varies depending on the engine rotation speed. Like this, the way of varying the opening/closing timing of an intake valve or an exhaust valve in accordance respectively with low speed or high speed of an engine in order to supplement the drawbacks of the general engine is called variable valve timing (VVT) method.
Unlike a prior camshaft, a camshaft-in-camshaft is not comprised of a shaft but a hollow camshaft, namely an outer shaft and a different shaft rotatably inserted therein, namely an inner shaft.
There are two kinds of cam lobes of a camshaft-in-camshaft, one kind of which are first cams fixedly installed on the outer shaft and the other kind of which are second cam fixed to the inner shaft and rotatable on the outer shaft.
A camshaft-in-camshaft structure has been devised such that among two types of valve connected thereto, one type of valve is moved unvariably in line with engine timing without special control and the movement of the other type of valve is controlled in order for a phase of the valve to become different from that of the former type of valve. A control apparatus varying a phase between a first cam and a second cam is called a cam phaser.
By utilize the camshaft-in-camshaft and the cam phaser, continuous variable valve timing (CVVT) method can be realized. The camshaft-in-camshaft a phase of which between a first cam and a second cam is varied by the cam phaser is generally called a control camshaft.
Generally, the control camshaft is fitted directly with the cam phaser such that the cam phaser can advance or delay (hereinafter, vary) a phase angle and, in other words, vary opening/closing timing of an intake valve or an exhaust valve. However, due to a layout structure in case of an engine's being actually mounted in a vehicle, a problem can happen in which the control camshaft can't be fitted directly with the cam phaser.
To overcome this problem, substantial changes in parts restricting the layout structure may be needed, but, they are very big task of changing not only the design of an engine but also entire package of the vehicle and come close to new development of an engine. In case of a remodeled engine, it's the case that to cope with the problem is almost impossible. Accordingly, a change in a structure and an installation position or an installation method of the cam phaser is required.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.